3,406,214 United States Patent Office Patented Oct. 15, 1968 2 the invention. Other objects and purposes will become 3,406,214 manifest subsequently. METHOD OF PREPARNG PERFLUOROETHYL ODDE The present invention is predicated on the rather un Walter Blochl, Karlsruhe, Germany, assignor to FMC Cor expected finding that perfluoroethyl iodide is readily and poration, New York, N.Y., a corporation of Delaware easily formed by contacting gaseous tetrafluoroethylene No Drawing. Continuation-in-part of application Ser. No. with liquid iodine pentafluoride at no more than about 475,282, July 27, 1965. This application Aug. 19, 1966, atmospheric pressure in the presence of a minor amount of Ser. No. 573,456 elemental iodine relative to the iodine pentafluoride and 5 Claims. (C. 260-653) recovering the so-formed perfluoroethyl iodide from the 10 reaction product. Generally speaking excellent results are realized by bubbling or introducing gaseous tetra ABSTRACT OF THE DISCLOSUIRE fluoroethylene through a liquid mixture of iodine penta fluoride and a minor amount of elemental iodine relative Perfluoroethyl iodide is prepared by introducing per to the iodine pentafluoride at atmospheric pressure and at fluoroethylene into iodine pentafluoride containing a minor mildly elevated temperatures, preferably about 40 C. to amount of dissolved iodine and isolating the so formed 80° C. perfluoroethyl iodide. The reaction of tetrafluoroethylene with the liquid mix ture of iodine and iodine pentafluoride to produce per fluoroethyl iodide in accordance with my new process This is a continuation-in-part of my copending appli 20 proceeds at a practical rate even after relatively short con cation Ser. No. 475,282, filed July 27, 1965, now aban tact periods. I have for instance achieved appreciable con doned. version of the perfluoroethylene to perfluoroethyl iodide This invention relates to perfluoroethyl iodide and in after a contact time of only one minute or so. Of course, particular to a method of preparing it by reacting per longer times result in proportionally higher conversions. fluoroethylene with iodine pentafluoride in the presence 25 An unusual aspect of the process herein is that it proceeds of elemental iodine. without significant quantities of by-products being formed. Perfluoroethyl iodide is a known compound which is In fact, the unconverted perfluoroethylene and perfluoro much used in the manufacture of organic fluorochemicals. ethyl iodide end product can be reintroduced through the It is, for example, a key starting material in the so-called liquid mixture of iodine/iodine pentafluoride until most telomerization reaction. The latter is a type of polymeri 30 of the perfluoroethylene has been transformed into per zation whereby perfluoroalkyl iodides of varying carbon fluoroethyl iodide without fear of ancillary reactions oc chain links can be built up by the successive reaction of a curring. In many of the known processes it is difficult to perfluoroolefin such as perfluoroethylene with perfluoro prevent telomerization from taking place, i.e., addition ethyl iodide. The resulting perfluoroalkyl iodides constitute of the perfluoroethyl iodide to the perfluoroethylene with a class of chemical intermediates which, because of the 35 iconcomitant build up of telogens of higher molecular reactivity of the iodine atom, are readily transformed into weight. My process is thus not critical in that it requires many useful and valuable fluorine-containing compounds. sensitive and delicate control to obviate formation of un In view of its role as a key fluorochemical intermediate, desirable by-products. The reaction conditions which I perfluoroethyl iodide has been investigated extensively, have discovered are thus unusually conducive to essentially particularly as regards its preparation, and numerous types 40 the sole formation of perfluoroethyl iodide. of synthetic procedures have been proposed. However, Moreover, the method of the invention requires no none of these are entirely satisfactory, at least so far catalyst or inhibitors and this constitutes a further im as commercial products are concerned. A method which provement and advantage over the hitherto practiced has received a great deal of attention and study is the processes using iodine/iodine pentafluoride and perfluoro reaction of perfluoroethylene with a combination of 45 ethylene. - iodine and iodine pentafluoride. Presumably, the iodine The amount of elemental iodine added to the iodine and iodine pentafluoride combine with one another to pentafluoride should not alter or materially change the form iodine monofluoride of the formula IF and this in liquid character of the iodine pentafluoride which melts turn adds to the double bond in the tetrafluoroethylene. at 9.6. C. and boils at 98 C. In this connection I have The process is commonly carried out by heating per 50 determined that the upper limit of elemental iodine is fluoroethylene and a mixture of at least two moles of ele about 50% of the weight of the iodine pentafluoride while mental iodine and one mole of iodine pentafluoride under the lower limit although not critical is for practical pur pressure in the presence of certain metals and/or metal poses in the neighborhood of about 1%. The preferred iodides as a catalyst. Such a process is disclosed in amount is about 10%. Where the amount of iodine is in U.S. Patent 3,006,973 to Hauptschein et al. An improve creased above 10% it sublimes out of the iodine/iodine ment or at least variation of Hauptschein's procedure pentafluoride mixture thereby causing clogging of equip utilizes a different type of catalyst system, preferably ment and generally interfering with the smooth operation antimony trifluoride. The latter process is the subject of the process. matter of U.S. Patent 3,132,185 to Parsons. Whereas the method of Hauptschein et al. requires inhibitors to prevent 60 The reaction of the perfluoroethylene with the iodine/ runaway polymerization with the more reactive species, iodine pentafluoride mixture is moderately exothermic. e.g. perfluoroethylene, the catalyst of Parsons on the It can be regulated and the preferred temperature range other hand obviates the need for inhibitors. However, realized by adjusting the flow rate of the perfluoroethyl both processes are objectionable in that high pressures ene. In some instances admitting the perfluoroethylene in are required. Perfluoroethylene is a hazardous material to 65 increments serve to conveniently maintain the optimum handle even under normal conditions. It is extremely temperature. Supplemental heat control is also useful sensitive and dangerous under autogenous pressure. and convenient in regulating the temperature. Thus, where I have now discovered a method of reacting perfluoro the perfluoroethylene passes through the iodine/iodine ethylene with iodine and iodine pentafluoride to give per pentafluoride mixture at a high flow rate, external cooling fluoroethyl iodide without the attendant disadvantages of 70 may be needed. On the other hand very low flow rates the prior known processes and the provision of such a will not normally necessitate external heating of the re method constitutes the principal object and purpose of action to provide optimum conditions. 3,406,214 3 : 4 According to the teachings of the prior art a high ratio cations and ramifications disclosed herein without depart of iodine to iodine pentafluoride is required to realize ing from the scope and spirit of the invention...... successful addition of iodine fluoride (IF) to the per Example 1 fluoroethylene double bond. Thus, both the Hauptschein et al. and Parsons patents specify a preference of at least A 100 ml, two-necked, pear-shaped flask was filled to two moles of iodine to one mole of iodine pentafluoride. /3 of its height with iodine pentafluoride having dissolved Such a ratio amounts to 230% of the weight of the iodine therein about 10% iodine based on the weight of the iodine pentafluoride or 23 times the 10% ratio used herein. In pentafluoride. 15.0 g. of pure, distilled tetrafluoroethylene fact according to the Hauptschein et al. patent iodine was introduced through the side arm of the flask at a rate pentafluoride containing small amounts of elemental of about 100 mls. per minute while maintaining the tem iodine functions essentially as a fluorinating agent and does IO perature of the iodine/iodine pentafluoride between about not give the desired perfluoroethyl iodide. By thus revers 60° C. and about 80 C. The gas was admitted through an ing the ratio of iodine to iodine pentafluoride and at the inlet tube extending to the bottom of the flask. The gases same time operating under mild temperatures without a emerging from the flask were collected in a cold trap catalyst or inhibitor and generally operating in a manner 5 maintained at -180° C. After all of the tetrafluoro counter to the prior art, I have achieved excellent yields ethylene has been bubbled through the iodine/iodine and conversion of perfluoroethylene to perfluoroethyl pentafluoride liquid the frozen mass in the cold trap was iodide without significant formation of by-products. At collected and subjected to fractional distillation. There the same time I have eliminated the hazard of working was obtained a low boiling fluorocarbon fraction and a with perfluoroethylene at super-atmospheric pressures. 20 residue of iodine pentafluoride. The low boiling fluoro Iodine pentafluoride is a known chemical compound carbon fraction amounted to 23.5 g. and contained 38% which is described in the usual chemical texts and period by weight unconverted tetrafluoroethylene and 61% by icals. It is commonly prepared by reacting iodine and weight perfluoroiodoethane. The conversion amounted to fluorine in the gaseous phase at a temperature of about about 40% and the yield about 90%. 150 C. It is a colorless liquid. 25 Example 2 As previously explained, my process of producing per fluoroethyl iodide is not critical in that the perfluoro The procedure of Example 1 was repeated but in this ethylene is merely passed through the liquid mixture of preparation the iodine was not dissolved in the iodine iodine and iodine pentafluoride. That is to say reaction pentafluoride but introduced in the form of a vapor along times do not have to be delicately adjusted to achieve a 30 with the tetrafluoroethylene gas. The results and yields product free of ancillary materials. It is, in other words, paralleled those obtained in the case of Example 1. self-regulating. Short contact times give low conversions What is claimed is: and high yields whereas longer contact times result in 1. A method of preparing perfluoroethyl iodide which high conversions and high yields. comprises contacting gaseous perfluoroethylene with liquid In practicing the process of the invention the gaseous 35 iodine pentafluoride in the presence of dissolved ele perfluoroethylene and liquid iodine/iodine pentafluoride mental iodine in a minor amount relative to the iodine mixture can be brought into contact with one another pentafluoride at about atmospheric pressure and at a tem using known procedures. Perhaps the simplest manner perature at which iodine pentafluoride remains liquid for a of conducting the process is to bubble the perfluoro sufficient period of time whereby at least part of the tetra ethylene through a vessel of the iodine/iodine pentafluoride 40 fluoroethylene is converted to perfluoroethyl iodide and and isolating the so-formed perfluoroethyl iodine from the recovering the so formed perfluoroethyl iodide from the exiting gases which consist of unreacted perfluoro reaction product. ethylene, iodine vapor, iodine pentafluoride vapor and the 2. The method according to claim wherein the perfluoroethyl iodine product. Another method of opera gaseous tetrafluoroethylene is bubbled through the iodine tion consists in admitting perfluoroethylene to a circulat pentafluoride. - ing or moving stream of the iodine/iodine pentafluoride. 3. The method according to claim 1 wherein the pres Elemental iodine and iodine pentafluoride are replenished sure is atmospheric pressure. as they are consumed. In fact my process is readily adapt 4. The method according to claim 1 wherein the able to the automatic production of perfluoroethyl iodide. temperature is from about room temperature to below In such a system the iodine/iodine pentafluoride is pumped 50 100° C. through a column or tube preferably a packed column to 5. A method of preparing perfluoroethyl iodide which increase surface area while perfluoroethylene is introduced comprises conducting gaseous perfluoroethylene through a countercurrently. The resulting mixture of perfluoroethyl liquid mixture of iodine pentafluoride containing a minor iodide, unreacted perfluoroethylene, iodine vapor and amount of dissolved elemental iodine relative to the iodine iodine pentafluoride vapor are conducted to a cooling 55 pentafluoride at atmospheric pressure and at a tempera station where the iodine/iodine pentafluoride vapors are ture of from about 40° C. to about 80° C. for a sufficient condensed and returned to the system while the perfluoro period of time whereby at least part of the tetrafluoro ethyl iodide and unreacted perfluoroethylene are separated ethylene is converted to perfluoroethyl iodide and re by fractional distillation or lead to a telomerization station covering the so formed perfluoroethyl iodide from the for conversion into higher molecular weight, telogens. 60 reaction product. Since the iodine imparts to the normally colorless iodine References Cited pentafluoride, a pink to brownish tint, electronic color UNITED STATES PATENTS sensing devices can be utilized to monitor and control 3,006,973 10/1961 Hauptschein et al. the iodine content of the iodine/iodine pentafluoride mix 3,132,185 5/1964 Parsons. ture in order to maintain the optimum ratio of com 65 ponents. Those skilled in the art will in general appreciate DANIELD. HORWITZ, Primary Examiner. that the process can be performed using various modifi